The present invention is directed to a method of decolorizing and stabilizing nitro compounds, in particular nitroparaffins, to provide a high grade product.
Nitroparaffins are commercially produced by vapor phase nitration of paraffin feed stock. The composition of the product stream depends on the paraffin feed utilized but is, in general, a mixture of nitromethane, nitroethane, as well as 1- and 2-nitropropanes. Vapor phase nitration of saturated hydrocarbons higher than methane are taught in U.S. Pat. Nos. 3,780,115; 3,869,253; 4,260,838; and 4,313,010 as well as an improved process of U.S. Pat. No. 4,458,094 in which a small amount of an oxygenated hydrocarbon is introduced as part of the feed stock. Production of specific nitro compounds has been achieved by contacting at elevated temperature and pressure, under homogeneous gas phase conditions a specific substrate compound selected from olefin, ketone, alcohol, or carboxylic acids with nitrogen dioxide alone or in the presence of oxygen and/or water as taught in U.S. Pat. Nos. 4,517,392; 4,517,393; 4,517,394; 4,524,226 and copending U.S. Ser. No. 649,765 filed Sept. 12, 1984.
The nitroparaffin products have been known to suffer from color development while being stored even over short periods of time. The identity of the colorizing materials nor the mechanism of their formation has ever been established. The removal of the colorants has been difficult to accomplish especially in view of the high activity of the nitro product, per se. The lack of ability to remove the color from nitro compounds has hindered their commercial usage even though they are known to be excellent solvents in a variety of applications.
U.S. Pat. No. 4,210,609 and Japanese No. 45-14048 teach a method of removing colorants from nitro paraffins by passing the nitro compound through a bed of activated alumina ('609) or distilling the nitro compound over a bed of activated alumina, aluminum fluoride or sodium silicofluoride. These processes have been known to exhibit spontaneous decomposition of the substrate causing catastrophic results.
It is highly desired to provide a method of treating nitro compounds to remove the colorants therefrom and to impart storage stability with respect to future color development.